The scientists also found that talking to friends and looking at a menu meant customers were less successful at getting served.

Gesturing with a hand or head to the barman was also not as successful as might have been expected, while holding a wallet or money in a hand did have some success.

While the findings might seem fairly obvious, the researchers, based at the Bielefeld University in Germany, conducted the work to help them develop a robotic bar tender.

They wanted to identify the body language that was most commonly used by customers and interpreted as someone wanting to buy a drink.

Dr Sebastian Loth, lead author of the study and a psychologist at Bielefeld University, said: “Effectively, the customers identify themselves as ordering and non-ordering people through their behaviour.

“Two signals are necessary and together form the sufficient set of signals for identifying the intention to place an order.

“First, the customers position themselves directly at the bar and, secondly, look at the bar/bartender.

“If one of these signals was absent, the participants judged the customers as not bidding for attention. This provided a clear indication that both signals are necessary for bidding for attention.”

The researchers, whose work is published in the journalFrontiers in Psychology, analysed 105 attempts to order drinks at nightclubs in Bielefeld and Herford in Germany and Edinburgh in Scotland.

They assessed the behaviour of customers 35 seconds before they were served.

They found the most successful tactic, which occurred in 95% of orders, was standing squarely towards the bar with head facing forward.

Looking at the bartender, was successful in 86% of the orders. Leaning on the bar happened infrequently but also seemed to high a high strike rate when it did happen.

Just one per cent of customers who were served had been looking at a menu, while three per cent were looking at the assortment of drinks on offer.

Looking at money saw just seven per cent of customers being served within the 35 second time frame.

However, the researchers did not assess how often customers employed unsuccessful techniques before they were served.

The findings were used to produce an update to the robotic bartender’s programming to allow it to ask customers if they would like a drink when they display the right body language.

The robot, called James, is being funded under a grant from the European Union.

“In order to respond appropriately to its customers the robot must be able to recognise human social behaviour,’ said Professor Jan De Ruiter, from the psycholinguistics research group at Bielefeld University.

“Currently, we are working on the robot’s ability to recognise when a customer is bidding for its attention.